Molar Volume of a Gas Lab

Today in class we worked on the Molar Volume of a Gas Lab. The goal of this lab is to measure the molar volume of Hydrogen gas at STP.

First, we measured out 10 mL of Hydrochloric Acid and poured it into the eudiometer.
Then, we filled up the rest of the eudiometer with water.
Next, we took a small strip of Magnesium and shaped it into a little ball and wrapped the Copper wire around it, which was placed in the stopper.
After, we put in the stopper and placed the eudiometer upside down in the stand, somewhat in a beaker half full of water.

The eudiometer's contents started to bubble, which is the evidence of the chemical reaction, and created the gas. The volume of the eudiometer minus the volume of the liquid left in the eudiometer equals the volume of the gas created by the chemical reaction.

In order to find the mass of the Magnesium strip, you have to use dimensional analysis to convert the length of the strip to grams using the conversion of 10 cm of Mg = 0.1407 grams.

The barometric pressure is 30.04 in Hg (inches Mercury), which you have to convert to millimeters.

Your water vapor pressure depends on whatever temperature you got.

Don't forget to use Dalton's Law of P(total) = P(H20) + P(H2), so that you can find the pressure of the Hydrogen gas to then find the molar volume. The total pressure is the barometric pressure, and the water pressure is your water vapor pressure.

The next scribe is Yada Thia.

Gas Stoichiometry

Hey Everyone! Today the lesson we learned was on Gas Stoichiometry. In class we went over our 

Ideal Gas Law WKSHT that was due today (answers posted on moodle). We then spent the rest of the period learning Gas stoich.

Stoich using PV = nRT

Mr Lieberman pulled out the mole cannon today and used it as our demo for today's lesson. Here's the video. (Don't know why you guys are so frightened?)

1. So in order to find the pressure of the gas in the tube you have to make and balance a chemical equation. So this is it for the mixture of the solid and gases in the tube.

CaC_2  (s)  + 2H_2 O ------>  C_2 H_2 (g) + Ca(OH)_2  (aq)    (sorry, underscore means subscript)

2. Next, you find the moles of gas formed from the reaction. Just a reminder, CaC_2 is the limiting reactant while the C_2 H_2 is the excess reactant.

   .37 g CaC_2              1 mole CaC_2               1 mole C_2 H_2

_____________  x   ________________  x  _________________  =     .006 moles.

            1                                64g                         1 mole CaC_2

3. Next, you have to find the pressure created by the gas. In order to do this, let's use PV=nRT!!

P=?      use PV=nRT     or    P= nRT/V

V=  .87L  (use the volume of cylinder that Mr. Lieb gave us)

T= 25 degrees Celsius + 273  =  298K  (Has to be in Kelvin)  (25 degrees is room temperature)

Moles=  .006 Moles   (work from above)

R=  .082  atm/moles K  (constant for gas)

Now that we have everything we need, we set up the problem!!!

       (.006) x (.0821) x (298K)  

P=  _____________________

      .87L

So in conlcusion, the pressure of the gas in the tube would be 0.17!

You could also solve stoich by using the Molar volume formula with STP. A.K.A. Standard Temperature Pressure

At STP, 1 mole of any kind of gas = 22.4L    (Molar Volume)

Sample Problem: Sodium azide is used in airbags to cause them to inflate on impact. What volume of nitrogen gas is formed from the decomposition of 1.00g of sodium oxide (NaN_3)? Assume STP conditions.

So first is the balanced chemical equation.

3 NaN_3 ------->  4N_2    +    Na_3  N

So we know this much....

T=273K

P=1 atm.

Let's use the formula

1.00g NaN_3        1 mole NaN_3            4 moles N_2               22.4L

____________ x ______________ x  ______________ x  ____________ = 0.46 

          1                           65g                  3 moles NaN_3         1mole N_2

See, you didn't have to use PV=nRT when you know you can sue STP! Time saver!!!

So that's pretty much what we learned in class today!

HMWK: Study for Quiz Tomorrow     (Good Luck on it!)

               Gas Stoich #1 WKSHT

               Ideal V.S. Combined WKSHT

The next scribe is Danielle Sindelar!!!  (Sorry to other people who wanted to be scribe)

Have a Great Thanksgiving Break!!!!!

Factors Affecting Gases

            Hi everyone. On Friday we had a very interesting lesson on the different factors that affect gases and how they affect them. These factors were pressure, temperature, and volume. There were several demos and explanations for these that I will  go over. I have pictures of the actual demos we did in class and not ones off the internet.

Boyle's Law
        The first three demonstrations were proving this law. The law states that as pressure decreases, volume increases or P1V1=P2V2 where P is pressure and V is volume.
               
Demo #1 Balloon in Vacuum Pump

 As you can see, there is a tube hooked up to the container that sucks out all of the pressure around the balloon. When this happens, the volume of the balloon increases...

 The same procedure is done with shaving cream and the result is the same.

Again, the pressure decreases and the volume increases...

 This was also done with a marshmallow, but unfortunately i could not get a picture. The same exact thing happened with that.

Charles's Law
         This law states that as temperature decreases, volume decreases, or volume is directly proportional to temperature. The formula for this is V1/T1=V2/T2 where V is volume and T is temperature.

The example of this was a demonstration that used liquid nitrogen, which is extremely cold, to lower the temperature of the air inside of the balloon resulting in a decrease in volume.

                                                                     

  Here the balloon is being stuffed into the liquid nitrogen. It takes a while for the balloon to deflate and shrivel up. It was difficult to get a picture of the shriveled up balloon because once it was taken out of the liquid nitrogen its volume started to increase rapidly because of the rise in temperature.

Gay Lussac's Law 
          This Law states that the pressure and temperature of a gas are directly related. The equation for this is P1/T1=P2/T2. 

To demonstrate this, and instrument that measures pressure was put into the liquid nitrogen to see if the pressure would lower along with the temperature.

         
         
         









Before the it was put in, the device read 15 atm and after it read 4.25 atm, so the pressure did decrease by a lot.

The Combined Gas Law puts all three equations into one, which makes it much easier to remember.
        The equation is P1V1/n1T1=P2V2/n2T2. P is pressure, V is volume, n is moles, and T is temperature. This equation is used in problems where there are two sets of variables, such as numbers 9, 11, and 12 in the homework.

Finally, there is the Ideal Gas Equation, in which the constants of the previous laws have been combined to form the gas constant R. This equation is PV=nRT where P is pressure, V is volume, n is moles, R is a constant for pressure (either 0.0821 atm L/ mol K or 8.314 kPa L/ mol K), and T is temperature. This is used in a problem where there is only one set of variables, which includes nearly all of the homework problems.

To end class on a good note, we had fun with liquid nitrogen and did activities such as watching Mr. Lieberman chuck frozen orange at the wall, pouring liquid nitrogen on the floor, and pouring it on Charles.

Homework: Ideal Gas Law worksheet and work on WA

The next scribe is.....Kevin L. who sits next to me

Gas Pressure and what it means in the Real World

Hello all, today in class discussed and demonstrated how gas and pressure are related. We did 3 demos, and although due to mitigating circumstances, neither video nor photos are available for you to view these demos, I think that my eloquent writing style better exemplifies these demos. Therefore, there were 3 demos on pressure, and we took some notes.

1.   Can Crushing 
http://www.youtube.com/watch?v=QVayky_b-6U

In this demo, we poured a little boiling water to can, then we put a flame under the can to heat it, then we put it upside down into the a bowl of water, and a there was slight "bang" and the can crumpled. One might wonder why this would occur, it seems to defy the laws of chemistry.  However, if one thinks this, then one does not really know the laws of chemistry at all in the first place, but only a select few do. As for the explanation, the can crumpled because the air pressure in the can is equal to the air pressure outside it. Thus there are no overall forces.  However, when the water is boiled, lots of steam is produced, which then pushes air out the can, until the can is completely filled with steam.  The steam has the same pressure as the air outside the can, so nothing occurs yet.  But once the can is placed upside down in the bowl of water, the steam cools and turns back into a liquid, and it thusly does not have the same pressure as the air outside the can.  The inside of the can becomes a vacuum, and with no pressure inside the can to fight the much higher air pressure outside the can, the air crushes the Coke can.  I also lied, i will be showing video and photos, just not from class.

2.  Stuck to the ground
http://www.youtube.com/watch?v=zqyuaMqOEGA
The  second demo, Mr. Lieberman put a vacuum device clamped onto a table and then onto the floor.  He then challenged anyone to try to lift up the device.  Because of the intense air pressure, no one without the use of performance enhancing drugs would be able to lift it up because the vacuum sucks up all the air.  When you lift up the clamps however, it is possible for you to lift it up, because the intense air pressure is let out.

3.  The  Vacuum
http://www.youtube.com/watch?v=Ct4AqODwhI8  In the third demo and final demo, Mr. Lieberman put someone in a plastic garbage bag with a very tight air seal.  With such a tight air seal, there was no air in the bag.  with no air in the bag, Alex the demonstrator began to feel more compressed and with nothing to resist, the air pressure outside the bag compressed on to him.  It was very interesting and one thinks we learned a lot because chemistry is better explained through demos than through lectures.






  Throughout the class we took some interesting notes on pressure.  We discussed some formulas and concepts on pressure in gases.

Formula for pressure:

We also learned some standard pressure units and values that include:

A. 1 standard atmosphere
B.101.3 kPa
C.760 mm Hg
D.760 torr
E.14.7 lbs/in2


Apparently you use these to convert from unit to unit.  One may wonder why there is not just one unit for all science, but that is merely wishful thinking.  Due to that, here is how you convert from pressure units.

I. Converting between atmospheres and millimeters of mercury.
One atm. equals 760.0 mm Hg, so there will be a multiplication or division based on the direction of the change.
Example #1: Convert 0.875 atm to mmHg.
Solution: multiply the atm value by 760.0 mmHg / atm.

Notice that the atm values - one in the numerator and one in the denominator - cancel, leaving mmHg.  So like in stoich, u want to the units to cancel, and once the units cancel, the rest is fairly easy multiplication done on a calculator.  It is important not to have a nervous breakdown about the complex-sounding units, for they merely sound and are written like that to inspire awe and wonder.  There you go, and I hope you learned a lot about pressure in gases.

Homework: Do pressure worksheet and begin completing webassigns unless they are not up yet, in which case, do not complete the webassigns, because it is technologically feasible.  I suppose you could make your own webassign and then complete that, but one doubts the likelihood of that. Thank you.

Next Scribe: Bram Hill who sits in the front row to the left.

Behavior of Gases

Today in class we learned about the properties of gases and had a few gas demos, after going over and reviewing our tests.

The first gas demo was with iodine crystals. The crystals were heated up and turned into a pinkish/purple color of gas.. There is a myth that since you cannot see gases, they are not real, which this experiment obviously proves wrong.

The next demo was with Hexane. Hexane evaporates very easily into the air, and the gas acts as if it is a liquid. After a little shaking, we were able to pour it down a pipe into a flame, igniting the flame and the rest of the gas coming down the pipe.

The final demo was with baking powder, acetic acid, and a candle. Two beakers, one empty, and one filled with baking powder, are presented. A lit candle is held in both of the beakers, but nothing happens. But when you pour acetic acid into the baking powder and it reacts, if you put the lit candle in it will extinguish due to the carbon dioxide from the reaction causing oxygen, which the flame needs, to be pushed out. This reaction makes the gas act like water and can be poured into the empty beaker, which will extinguish a lit flame as well. The final part of the demo with the tube and the carbon dioxide did not work so well, but was meant so that gravity pulls carbon dioxide into an empty beaker where the candle can be extinguished.

Homework: Gases Chemthink and Behaviors of Gases worksheet.

Next scribe will be Zach Salty

Colligative Properties

Colligative Properties are properties of substances such as vapor pressure lowering, boiling point elevation,melting point depression, and osmotic pressure. The main ones we will focus on is boiling point elevation and melting point depression. Also, these properties are only changed by the number of solute particles, not by the identity of the solute.

Boiling Point Elevation

The boiling point elevation property is simply this, ΔTb(subscript) = Kb(subscript) x m. ΔTb is added to the normal boiling point to get the new boiling point. Kb is the constant which will be given to you. m is the molality. That is how you figure out the boiling point when adding one substance to another.

Freezing Point Depression

The freezing point depression property is, ΔTf(subscript) = Kf(subscript) x m. The symbols in the equation meant the same thing as above. Again, the constant (Kf) will be given to you in problems. Below is an experiment that we did in class. First, Club Soda was chilled to about -8 degrees Celsius. This was done by adding normal table salt to ice making the freezing point of the water go way down, this enabled the water and ice to get very cold. Then when the Club Soda was removed from the water the bottle was opened to release the carbon dioxide and flash freeze the soda.

HW: Solution Concentration WS

The next scribe is: Jake A.

Molarity/dillution

Hello all, today we went over molarity and dilution.  Using molarity is pretty simple if you follow some easy steps.

Primero, remember that molarity= moles solute/liters of solution

Por ejemplo, if you have an equation like : Dissolve 4.00 g of NiCl2 x 6H20 in enough water to make 150 mL of solution.  Calculate the molarity, so first we do what we learned in stoichometry last unit, 4.00 g x 1 mol/ 237.7 g (which is the molar mass) and you will get 0.0168 mol. 

 Entonces you simply follow the formula mentioned previously: 0.0168 mol (the moles solute you found) / 0.150 L (after you convert milliliters to liters) and your final answer is 0.112 M.

For using molarity, remember that moles= mass x volume so simply make any necessary conversions in any given equation, the do the calculations to find moles.  once moles are found.  Convert the moles to grams by multiplying the mols by the g/mol. that is ur final answer.

Ademas, 2 other ESSENTIAL concentration units is Molarity, m which is  :  m of solution= mol solute/ kg solvent
and % of mass= grams solute/ grams solution.  Basically, if you understand the formulas and know them relatively well, all you have to do is make sure your conversions are correct, and you put the numbers in the right places to be multiplied or divided,

Tambien, it is necessary to understand that diluting a solution is just adding more water and therefore the amount of solute stays the same.  Henceforth nb =na  and n= MV .   MbVb=MaVa

Very important in dilution equations is to first find all the variable you know for sure. for example, if in a given equation M1, V1, and V2 are given for sure. all you have to do is simple algebra to solve for M2. once you get M2 you put all 4 variables back into the equation and  ipso facto you have your answer.  In our level of chemistry you are almost always given 3 variables and thus you only have to solve for one.  Don't get caught up over the different letters for variables, because that is just the chemistry gods trying to mess with your brain.   

Finalmente, molarity and stoichiometry equations are literally the same things as mentioned previously.  just find out all the variables you know for sure, solve for the variable you dont know. and make all the necessary conversions.  If you did not receive a 61.6 % on a test like some people did, you should understand it pretty well.  That is all for today, and I hoped i somewhat atoned for my good, but not spectactular showing yesterday.

Hw: Molarity worksheet and begin doing webassigns

Next Scribe= Cody from Stage crew

  

Solubility of Common Compounds

Hello all!

Our class today began with a recap of yesterday's solubility lab. We were showed some tricks for equation balancing and determining solubility before we delved into today's main lesson.

Our main lesson today was the rules for the solubility of common compounds. We learned that certain compounds are soluble in water, unless containing certain ions that make them insoluble. For example, compounds with Chloride, Cl-, are soluble in water unless they contain the ions Ag+, Hg2+2, or Pb2+.

Inversely, some compounds have rules in which they are insoluble in water unless they contain certain ions that make them soluble. For example, sulfide compounds, S2-, are insoluble unless they contain ions of K+, Na+, or NH4+.

We had the rest of the class to work on the lab or the 1st Reaction Solubility worksheet.

The next scribe will be Zach(Salty).

Unit #4 - Solubility Rules Lab

Wednesday, October 31, 2012

HAPPY HALLOWEEN!

There were some great costumes today! Mr. Leiberman had a stellar Captain America costume on!

We started off class by checking in our two homework assignments. If you missed class, need the worksheets, or the answers, make sure to refer back to our Moodle site for all those links!

We spent the second half of class on our Solubility Rules Lab. We mixed six different sodium solutions with eight different nitrate cations to see which reactions would create a precipitate. We looked for "cloudiness" to help determine if a precipitate formed. Just looking at the color change was NOT enough to distinguish a precipitate.

The anions were sodium...

• carbonate
• chloride
• hydroxide
• iodide
• phosphate
• sulfate

The cations were nitrates of...

• aluminium
• potassium
• barium
• calcium
• copper (II)
• iron (III)
• silver
• zinc

It was a quick and organized lab, so we spent the last 10-15 minutes of class working on the post-lab questions. Also, since some people did not know who Captain America is, we watched a trailer of Captain America: The First Avenger.

Remember, the lab is due Friday! Have a great November!

The next scribe will be... Jake Aquino!